Spatial variability in forest fuels: Simulation modeling and effects on fire behavior

Forests in the western United States and elsewhere face a growing crisis arising from global warming, changes in fuel beds and an increasing human population. Fire management policy emphasizes fuel treatments, such as thinning and prescribed burning, to remedy this situation because fuels are the one component of the problem that we can directly affect through management action. At present, however, the tools we have for the evaluation of fuel treatments are inadequate because they do not describe the fuel bed, or effects of modifications to the fuel bed on fire behavior in sufficient detail. The work described here presents a system that has potential to address the shortcomings of current approaches. In the first chapter, to improve our ability to represent wildland fuels, a three dimensional spatially explicit fuel model, FUEL3D, is presented which represents fuels at a level of detail comparable to what we can actually measure: stands as collections of individual trees, with branches and foliage. In conjunction with new, physical fire models, detailed fire behavior simulations can be carried out using fuels represented with FUEL3D as inputs. This system thus comprises a simulation laboratory which will greatly enhance our capabilities to evaluate fuel treatments and strengthen our understanding of fire and fuel interactions. In the second chapter, this system is demonstrated in an exploratory simulation study which examines the impact of spatial variability within an individual tree crown on fire behavior. Results demonstrate that the distribution of fuel within a tree crown significantly affects the rate of fuel consumption, as well as the timing, duration and magnitude of heat produced. This suggests that modeling of both crown fire initiation and propagation would benefit from more detailed description of crown fuels. In third chapter a replicated series of stand scale fire simulations is carried out to examine variability in forward spread rate; accelerated spread rates endanger fire fighters. Substantial variability is observed to arise from fine scale fuel-atmosphere-fire interactions which are not easily predicted beforehand. A new strategy is proposed in which physical fire models are used to quantify the potential drivers of variability in fire behavior